K2AV seem to be a storehouse of information. Thanks again Guy.
One point, K2AV said:
"If you model a real BOG, you find that beyond an ELECTRICAL half wave ON
THE WIRE, or two hundred something feet on 160, extending the BOG wire will
start to REVERSE the pattern."
That never happened with my 366 ft BOG when it was lying on dead grass
at an average of about 1.5 inches above the dirt. My tests comparing a
250 ft BOG to a 366 ft one showed no significant front to back
difference. There were some pattern differences in other directions.
I have never put a BOG directly on dirt so I can't say what happens
there. Measured data with the BOG 1.5 inches above the dirt does show
that BOG gain drops about 6 dB right after a heavy rain or about the
same when covered by an inch of snow. Normally the gain of both the 250
and 366 ft BOGs were at about -17 dBi measured by comparison to another
antenna that I know the gain of.
I do know where the 250 ft recommended length for a 160 BOG came from.
It came from NEC. I can make those same conclusions too if I only look
at NEC data. I originally decided on 365 ft because NEC said it was
better than 250 ft. Subsequently I have lost confidence in NEC being
able to calculate BOG performance at any length. That was the impetus
for my tests comparing 250 to 366 ft.
K2AV also said:
"A "beverage" ON the ground really is NOT a beverage."
I agree that there is a lot of difference between a BOG and a Beverage
above ground. At least that's the way we refer to them now but did you
know that the antenna invented by Harold Beverage was a wire lying on
the ground? Here is an excerpt from an interview with him:
Beverage's words:
"I invented the receiving antenna, the groundwave, the long waves laid
on the ground. They were unidirectional, and nobody knew why. Others —
the Navy — had used the ground waves, too. So I took a big heavy
receiver down the line and broke into some wires to see how the signals
built up as it went towards the north and the static went down. Then
going the other way, the signal went down and the static came up. Well,
I discovered that the reason that that antenna wire laying on the ground
was unidirectional was the high losses. So that the static had built up
to the northeast end and never got back down to the southwest end into
the receiver. It was unidirectional just simply because of the losses of
the wire laying on the ground. The idea then was we put stuff on wires
at the northeast end. There was a resistor equal to the impedance of the
antenna to make it unidirectional. You had but one wire I think."
Jerry, K4SAV
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